Let There Be Dark—and MelatoninWe are learning that darkness and a good night's sleep are much more important than we had thought
By Hyla Cass, M.D.

ecause we are creatures of the light, there is something peculiarly menacing about the night hunters of the natural world—predators that prowl in the dark, often using senses other than vision to help guide them to their hapless prey. It was not that long ago in evolutionary history that we were prey, and the nighttime was filled with silent terrors. After a long, hard day of hunting and gathering, our ancestors would huddle together for safety, such as it was, to endure another night of uneasy sleep, always mindful of the hungry beasts out there … perhaps close by … that they could not see.

Imagine how thrilled those early humans must have been when they learned how to make a campfire and could sleep close to it for its comforting warmth and even more comforting light. Probably no discovery or invention in history can compare with fire in terms of bettering the human condition. Fire enabled our ancestors not only to cook their food and stay warm, but also, perhaps best of all, to hold the demons of the night at bay. What a blessing!

How a Great Thing (Light) . . .

The taming of fire also did something else, though: for the first time in the history of any living thing, it altered the natural cycle of light and dark. Suddenly, our ancestors were able to see 24/7, just by keeping a fire going. It was an epochal achievement, but it may have set the stage for certain kinds of trouble that they could not have imagined and that did not become manifest for a very long time.

Flash forward about a million years, from their time to that of our grandparents or great-grandparents, most of whom were born into a world that had changed little, in terms of the light/dark cycle, over that vast expanse of time. For them, as it had for tens of thousands of generations before them, the day began at dawn and ended at dusk, and the only illumination they would have for the rest of the night was the soft glow of candles or oil lamps or fireplaces. Sure, they could stay up for awhile and read or play games, but with that low level of light, and with no Leno or Letterman to look forward to, pretty soon they went to bed, had sex, and went to sleep—in a really dark room, with no night light.

. . . Became Too Much of a Great Thing

Then came Thomas Edison, and everything changed. Indoors, and even outdoors, the night could be made as bright as day. Suddenly, we could do almost anything we wanted, whenever we wanted, wherever we wanted. And did we ever! We took to nightlife—in our homes, offices, factories, playing fields, and, yes, nightclubs—as if born to it. Little did we know, however, that by doing so, we were inviting a variety of medical ills directly attributable to something that had never existed before to any significant degree: too much light. The taming of fire long ago may thus have provided the first example in history of what we now know as the law of unintended consequences.

It's not so much that light is bad for us as that darkness is good for us. Thus, not getting enough darkness can be harmful to our health. That's odd, isn't it? Our ancestors would surely not have understood this paradox, but we are beginning to understand it, thanks to medical research that has shed new, uh, light on the subject of darkness.

Darkness Produces Melatonin

With nothing more dangerous than a kitty cat stalking us as we sleep, we can, and should, consider darkness to be our friend, physiologically speaking. The reason is that darkness—or, to put it the other way, the absence of light—stimulates the production of a hormone, melatonin, from its immediate precursor, the neurotransmitter serotonin. Like serotonin, melatonin plays important roles in our physical and mental well-being. Well discuss some of those shortly, but first let's see how our production of melatonin is controlled.

When light enters our eyes, photoreceptor cells convert it to nerve impulses that travel via the optic nerve to the brain. They go not just to the visual cortex, where they are processed to produce the sensation of vision, but also to two clusters of neurons called the suprachiasmatic nuclei (SCN). Together, these nuclei constitute the body's circadian pacemaker, popularly known as the biological clock, which regulates many aspects of our physiology on a 24-hour cycle. The pacemaker monitors the incoming light levels and sends relevant information to the pineal gland, buried deep within the brain. This pea-sized gland responds by adjusting the brain's output of melatonin accordingly.

During daylight hours, melatonin production is minimal, and blood levels of this hormone remain low. When night falls, however, and the ambient light level plummets, the absence of light induces biochemical changes that cause melatonin production to increase dramatically, about 2 hours later. That's when we begin to feel sleepy, the signal that it's time to go to bed. Melatonin levels peak during the night and then decline to their previously low levels by morning—time to wake up.

Instead, We Turn on the Lights

In an ideal world, we would go with the flow of nature's circadian rhythms, obeying the melatonin signal by going to bed and getting a good night's sleep (which for most people means 7 to 9 hours, depending on individual needs). Alas, however, our modern world is far from ideal in this regard. When night falls, we turn on the lights, thereby suppressing the melatonin signal and interfering with the circadian rhythms that millions of years of evolution have programmed us for. Instead of getting ready for bed, we keep on working or playing, doing chores, pursuing hobbies, watching TV, etc. For some of us, actually, our day is just beginning, as we prepare to go to our night-shift jobs, where we'll be exposed to bright light all night long.

Our poor biological clocks get thrown out of whack by all this. In a very real sense, we are fooling Mother Nature, and, as everyone knows, that's not nice. It's also unhealthy. The most obvious casualty is adequate and restful sleep. With our busy, fast-paced lifestyles, and with deficient levels of melatonin in our systems during the night, we sleep poorly and not enough. The result is a population that is chronically and dangerously sleep-deprived, with consequent fatigue, irritability, depression, impaired reflexes, and susceptibility to accidents, just to name a few. Night-shift work exacerbates most of these problems and is seen as a serious threat to the workers' health. Poor or inadequate sleep can even lead to premature death.1*

The elderly are especially prone to sleep disorders because, as with many other vital hormones, our ability to produce melatonin declines sharply with age (obesity is another culprit in this regard). In a recent review of the clinical uses of melatonin by researchers in Argentina, the authors stated,2

Aging has been associated with a significant reduction in sleep efficiency and continuity and coincides with a significant reduction in amplitude of the melatonin rhythm. Increase in early morning awakenings and difficulty in falling sleep [sic] have been frequent [sic] reported in the elderly. Impaired melatonin secretion has been shown to be associated with the sleep disorders that are encountered in elderly insomniacs. Indeed, aging may be a process resulting in part from relative melatonin deficiency, and melatonin can be effective for improving the quality of life in the elderly.

They go on to discuss some of the physiological functions that are influenced by melatonin, which they refer to as a chronobiotic agent because its effects oscillate rhythmically with the status of the biological clock. Among these functions are sleep regulation, immune function, inhibition of tumor growth, blood pressure regulation, retinal physiology, control of mood and behavior, and free radical scavenging (melatonin is a strong antioxidant, as are several of its metabolites). Most of these functions are relevant in both normal and pathological aging.

Alzheimer's Disrupts the Sleep/Wake Cycle

Among the most notorious pathologies related to aging is dementia, of which Alzheimer's disease is by far the most prevalent kind. A characteristic symptom of this disease is severe disruption of the sleep/wake cycle. The Argentinean researchers point out that this is believed to result from damage to the suprachiasmatic nuclei, causing the patients' melatonin secretion to be highly irregular.

Many Alzheimer's patients exhibit a sleep disturbance called sundowning, which is a worsening of cognitive functions and an increase in behavioral anomalies during the evening and nighttime hours. The pattern includes increased confusion, agitation, inattention, restlessness, pointless repetition, and wandering, among other things. Naturally, this can add greatly to the caregivers' burden, often making it impossible for them to get a good night's sleep as well.

Melatonin Helps with Sleep and Memory

With abundant clinical evidence of the strong correlations between melatonin deficiency and Alzheimer's disease (even in its earliest, preclinical stages), it makes sense to try to alleviate Alzheimer's-related sleep disturbances, including sundowning, with supplemental melatonin. The Argentinean authors discussed nine such studies, with melatonin doses ranging from 2.5 to 10 mg/day. All of them had produced positive results, including, in some cases, improvements in memory. In reference to five of the studies, the authors stated that the declines in cognitive functions that one would expect to see in untreated patients were halted by melatonin.

They also discussed a number of studies demonstrating strong neuroprotective mechanisms of melatonin, one of which is its antioxidant activity, mentioned above. They mentioned melatonin's more general cell-protecting properties as well, citing its very strong cytoprotective activity in situations such as osteoporosis, ischemia-reperfusion (the restoration of blood flow after an occlusion, which causes oxidative damage to blood vessels and tissues), and diabetic microangiopathy (the damage done to capillaries as a result of diabetes).

Melatonin Protects Against Brain Damage

Most intriguing, however, is melatonin's ability, in numerous animal experiments, to prevent the neurotoxicity of amyloid-beta, the protein that is the principal constituent of senile plaques. These harmful deposits, a hallmark of Alzheimer's disease, attack and destroy neurons, resulting in the substantial loss of brain matter seen in Alzheimer's victims at autopsy. They also stimulate the production of another pathological feature of the disease, neurofibrillary tangles, which contribute to the same dreadful outcome.

The authors concluded,

Melatonin may provide an innovative neuroprotective strategy in normal and pathological aging. Melatonin protects against several mechanisms of neuronal death … Through restoration of slow-wave sleep, melatonin treatment can result in better regulation of neuronal metabolism. Indeed, better sleep must be considered as a neuroprotective strategy that can potentially improve the course and outcome of several brain disorders associated with aging, and thus the quality of life of the affected individuals and their family members. To promote and protect an appropriate sleep can substantially reduce the costs of treatment and management—in particular, the enormous costs of lifetime treatment of some neuropsychiatric disorders.

More Melatonin, Please

Scientific studies on the use of supplemental melatonin for improving sleep have generally used dosages in the range of 0.3 to 5.0 mg/day. Melatonin is best taken shortly before bedtime, because it usually takes effect about 30 minutes after ingestion. It gradually leaves the circulation during the night, and by morning, it's virtually gone. Its worth noting that melatonin is nontoxic and very safe—much safer than prescription sleeping pills, which can have dangerous side effects, particularly in those over 60 years of age.

How bizarre it is to think that here, in the twenty-first century, one of the demons of the night that we have to contend with is light, the very thing our primordial ancestors must have craved most during those long, scary nights in the jungle or savanna. Imagine how astounded they would be if they could see the luminous world we live in and hear our cries for more darkness—or, at least, more melatonin.

Blind women tend to have high average melatonin levels (because they live in a permanent state of darkness), and they have unusually low rates of breast cancer. Sighted women who happen to have above-average melatonin levels are also unlikely to develop breast cancer. Does this prove anything? No, but it's intriguing. Add to it that women who work night shifts and therefore have low melatonin levels (because they're exposed to bright light all night long) have about a 50% greater risk for breast cancer than other working women. That still doesn't prove anything, but now it's extremely intriguing.

A link between nighttime light-induced melatonin deficiency and breast cancer had long been suspected, but strong experimental evidence was lacking—until now. An article in Science News reports on the results of several studies showing that the link is almost certainly not just a coincidental correlation, but a genuine cause and effect.1

The centerpiece of the research was an ingenious experiment conducted at the Bassett Research Institute in Cooperstown, New York. Scientists implanted human breast tumors in rats in such a way that the rats' blood circulation to the tumor could be shut off temporarily in favor of an outside source of blood, which was introduced through the only artery supplying the tumor and extracted through the only vein draining it. In this way, the living tumor could be biologically isolated from the rat. Any effect of the outside blood on the tumor (as determined by the tumor's effect on the composition of the blood) would thus be attributable to the blood donor alone, with no contribution from the rat. Very clever!

The donors were a dozen women volunteers, who gave blood once during the day, when their melatonin levels were low, and twice during the night: first after 2 hours of total darkness (when their melatonin levels were high) and then after spending 1 1/2 hours staring at a brightly lit white wall (this would suppress their melatonin levels).

The results were dramatic: the tumor cells proliferated most rapidly when the blood had little or no melatonin content (daytime and brightly lit nighttime samples), and they stopped proliferating when those samples were artificially spiked with melatonin. By contrast, the tumor cells did not proliferate when the blood had high melatonin content (darkness samples), but they could be made to start proliferating by spiking those samples with a chemical that blocks melatonin's activity.

These experiments provide compelling evidence that bright nighttime light, by suppressing melatonin production, is a risk factor for breast cancer. It's not unlikely that the same might be true for other cancers as well. Perhaps we would all benefit from spending more time in the dark—literally.

For those who are concerned about the quantity and quality of their sleep, along with the many health benefits that a good night's sleep can provide, melatonin, the natural hormone that governs the body's sleep/wake cycle, is a good idea. Disruptions of this cycle can be deleterious in numerous ways. Through its sleep-promoting effect, melatonin may be beneficial for cognitive function in the elderly.
Melatonin may also be taken combined with the melatonin precursor 5-HTP (5-hydroxytryptophan), which has calming effects, and choline, a precursor to the neurotransmitter acetylcholine, along with their vitamin cofactors. Finally, an extract of the adaptogenic herb Rhodiola rosea may add an extra dimension of versatility, whose health benefits may extend beyond those of a good night's sleep.

Dr. Hyla Cass is a nationally recognized expert in integrative medicine, an assistant clinical professor of psychiatry at the UCLA School of Medicine, and the author or coauthor of several popular books, including Natural Highs: Supplements, Nutrition, and Mind-Body Techniques to Help You Feel Good All the Time and 8 Weeks to Vibrant Health: A Woman's Take-Charge Program to Correct Imbalances, Reclaim Energy, and Restore Well-Being.